Part of this difference is because different animals have different
nubers of neurons, and different numbers of synapses between each neuron.
Another problem is that right now it is not possible to count the number
of synapses on a mammalian neuron, so instead scientists make estimates.
Since the scientists have to decide how to make the best estimate, this is
a little harder to understand: http://marlin.li
fe.utsa.edu/Tony_June1998/page.html You can think about
how the number of synapses changes how the neuron works by playing around
with a model of a set of neurons that synapse together. Here is one
model: http://www.
tiem.utk.edu/~harrell/webmodules/synapse.html